1. Field of the Invention
The present invention relates to chemically resistant gasket material, and particularly stiffened fluoropolymer gasket materials.
2. Description of Related Art
Expanded polytetrafluoroethylene (PTFE) is widely employed today in a variety of gaskets and other sealing applications. As is disclosed in U.S. Pat. No. 3,953,566 to Gore, this material has numerous properties making it highly desirable as a gasket, including: being readily compressible and conformable; being chemically resistant; having relatively high strength; and being far less prone to creep and loss of sealing pressure than full density PTFE. Gaskets made from PTFE are commercially available from a number of sources, including W. L. Gore & Associates, Inc., Elkton, Md., under the trademark GORE-TEX.RTM., Inertech, Inc., Erlanger, Ky., under the trademark INERTEX.RTM. and Garlock, Inc., Palmyra, N.Y. under the trademark GYLON.RTM..
While gaskets formed from pure expanded PTFE perform very well in many gasket applications, these gaskets have a number of deficiencies. One problem with this material is that it is extremely flexible. This flexibility makes the gasket difficult to handle and/or install in many instances, especially where sealing surfaces are in awkward locations or where the gasket may be prone to bending or folding during installation.
A number of solutions have been proposed to address these problems. Some manufacturers have attempted to stiffen the expanded PTFE material by attaching the expanded PTFE to a stiff substrate of metal or similar material. While a metal substrate improves handling characteristics, it tends to constrain possible uses for the gasket, leaving the substrate material subject to attack by harsh chemicals or other environmental factors. One gasket of this type employing a stainless steel core is available from M&P Manufacturing Inc., Freeport, Tex., under the trademark TEPHONIC.RTM..
Garlock Inc. has attempted a similar approach with its ENVELON.RTM. gasket. In this instance, the gasket comprises a compressible outer layer containing microballoons surrounding a solid, sintered PTFE material in its middle to prevent media permeation and blowout. This material is apparently disclosed in U.S. Pat. No. 4,900,629 to Pitolaj. However, since the microballons in the ENVELON.RTM. gasket are not made of PTFE, the gasket may not be as chemically resistant as may be desirable.
Another approach attempted by some has been to load the expanded PTFE material with a filler that supplies some limited rigidity. Examples of fillers placed into some gasket materials that may supply some limited rigidity include glass microspheres and inorganic microspheres, such as silica and fiberglass. While limited additional rigidity can be supplied in this manner, these fillers tend to diminish the overall performance of the gasket material--limiting chemical or temperature resistance or other qualities.
Still another solution to the problem of insufficient rigidity has been developed by W. L. Gore & Associates, Inc., in its insertable GORE-TEX.RTM. gasket product. This gasket comprises a ring gasket constructed entirely from expanded PTFE that has a raised sealing surface and a densified area next to the sealing surface that supplies rigidity to the gasket. As such, the gasket has the advantages of PTFE, such as chemical resistance and good sealing characteristics, while being far easier to install in many applications.
Unfortunately, the structure that provides the improved handling characteristics of the insertable GORE-TEX.RTM. gaskets restricts their use in other sealing applications. Insertable gaskets are selectively densified during manufacture to achieve rigidity. As such, these gaskets are not capable of ready modification by the user. Further, unless mounted under high stress, these gaskets do not supply a wide sealing area over the entire gasket face. Conventional expanded PTFE sheet gasketing, however, may be trimmed and modified by the user to address particular sealing needs. Another advantage of these gaskets is that the entire gasket material placed between sealing surfaces serves as a seal.
Accordingly, it is a primary purpose of the present invention to provide a sealing material with the operating advantages of PTFE while being sufficiently rigid so that it can be easily handled and installed.
It is a further purpose of the present invention to provide a rigid PTFE sealing material that has a wide, conformable sealing surface.
It is another purpose of the present invention to provide a rigid PTFE sealing material that can be supplied in a sheet or other form that can be readily customized by a user without compromising gasket integrity.
These and other purposes of the present invention will become evident from review of the following specification.